Generally, a solar cell is a semiconductor device to generate electric power from sunlight. Spectral responsivity and indicators such as open circuit voltage, short circuit current, conversion efficiency, maximum output, and the like are main factors determining solar cell performance and selling price. These performance indicators are determined by measuring photoelectric characteristics like current-voltage curve or spectral responsivity, which a solar cell outputs, under the condition of maintaining a constant device temperature (25±1° C.) after exposing the solar cell to light having a specific spectrum (AM 1.5 G) and photo-irradiation intensity (1 sun=100 mW/cm2) that International Standard provides, and the aforementioned test condition is called Standard Test Condition (STC).
In this case, a conventional measurement device for current-voltage curve or spectral responsivity of a solar cell used an indirect method for controlling a sample temperature, which controls a sample temperature by controlling a temperature of a sample stage to which a measurement target solar cell is fixed, to maintain a temperature of a solar cell device at a value similar to STC conditions during measurement.
In the case of a general crystalline silicon solar cell whose thermal conductivity is relatively good, and a thin film solar cell using thin glass substrates or metal substrates, the indirect method for controlling a sample temperature is fully efficient because an effective heat exchange between a sample stage and a sample is possible.
However, in the case of a thin film solar cell using thick glass substrates or a solar cell that has to use an additional jig for measurement, because heat exchange between a sample stage and a sample is not effective, a temperature of the solar cell sample increases steeply when it is exposed to light, and it is not easy to maintain the temperature of the measurement target solar cell at a value similar to STC conditions. Also, in the case of a dye-sensitized solar cell, which requires a relatively long time for measurement due to slow spectral response time since it should be exposed to light for a longer period of time for measurement than other types of solar cells, shortcomings of an indirect method for controlling a temperature stand out.
Furthermore, as an accurate measurement is difficult due to the sample temperature increase caused by photo-irradiation or other reasons in the procedure of measuring photoelectric characteristics of other manufactured samples besides a solar cell. Efforts to solve the problem are ongoing.